Candoluminescence is the light given off by certain materials that, when heated to incandescence, emit a larger proportion of their radiation in the shorter-wavelength visible spectrum rather than infrared, compared to a blackbody at the same temperature. The phenomenon is noted in certain transition metal and rare earth metal oxide materials (ceramics) such as zinc oxide and cerium oxide or thorium dioxide, where some of the light from incandescence causes fluorescence of the material. Quicklime (calcium oxide) also has this effect, called limelight in this case. The cause may also be due to direct thermal excitation of metal ions in the material. Candoluminescence may also sometimes be used informally to describe any material heated to incandescence specifically by a flame. The most common examples of candoluminescence can be found in the glowing cerium/thorium (ratio of ~1:99) oxide mesh of a kerosene lamp mantle or gas mantle and in an old style limelight.
It is not clear that a separate physical phenomenon called candoluminescence is required to explain the behavior of Welsbach mantles or limelight. Thorium oxide has very low emissivity in the near infrared region than the shorter wavelength parts of the visible spectrum. Without cooling by infrared radiation, a mantle can get closer to the flame temperature than can a black body material. The higher temperature leads to higher emission levels in the visible portion of the spectrum. Cerium dioxide was made part of the mantle composition to enhance radiative cooling by the emission of visible light.